1. Field of the Disclosure
The present disclosure provides a composition useful for Minimum Quantity Lubrication (MQL) during machining of a metal part. In particular, the present disclosure provides a composition which uses specially prepared exfoliated nanoparticle graphite platelets which enable stable mixing with the machining oil before or during the machining. The exfoliated graphite platelets can be prepared by microwave or radio frequency heating during removal of an intercalating agent between layers of the graphite and then pulverizing the exfoliated platelets without the agent to produce an exfoliated platelet with a thickness in the nanometer range between 0.1 nanometer to 100 nanometers and a platelet diameter in the range of 0.1 microns to 200 microns.
2. Brief Description of Related Technology
Cutting fluids have been widely used in metal cutting operations to extend tool life, improve surface finish and remove chip away from the cutting zone. In spite of the superior performance in using cutting fluids, some important concerns limit their usage. One of the major concerns is related to its disposal and subsequent negative impact on the environment. In that regard, new government policies have pointed towards the reduction or total elimination of cutting fluids. In addition to environmental concerns, the reduction or elimination of cutting fluids brings economical benefits for companies by reducing recycling operation and disposal cost.
Dry machining could be the ultimate solution that eliminates environmental and health concerns. However, the generation of particulate by-products and the ineffectiveness are the major drawback in the metal cutting process, especially when fine surface finish and aggressive cutting conditions are required [Sreejith 2000, Wakabayashi 2006]. In some operations such as machining aluminum alloys and stainless steels, cutting fluids are indispensable to avoid tool-work adhesion and built-up edge formation. In the particular case of cast materials, where low cutting forces and temperatures are expected, dry-machining is only possible for limited cutting conditions with certain types of cutting tools [Klocke 1997]. Thus, the ideal solution in the cutting fluid usage lies between dry machining and flood cooling. In this context, Minimum Quantity Lubrication (MQL) has been introduced as a viable method to practical machining processes.
MQL research is still in its infancy, and no clear direction has been established regarding the important parameters defining its effectiveness of MQL. Some researchers have focused their efforts to find the optimum type of lubricant in several works. For example, Heinemann et al. [2006] found that the mixture of water and a synthetic lubricant provided the longest tool life in deep-hole drilling. Wakabayashi et al. [2006] compared the MQL performance of synthetic esters and vegetable oil. The importance of these lubricants for MQL resides in their biodegradability and oxidation stability. Lopez et al. [2006] concluded that the optimal nozzle position in end milling formed a certain angle with the feed direction where the coolant can penetrate the cutting zone more efficiently. In fact, the tool wear reduction was observed when the oil mist was sprayed into the tool insert just before engagement. They also observed that by increasing oil flow rate flank wear was improved. Ueda et al. [2002] found that the appropriate nozzle orientation has a significant effect on reducing the cutting temperature on rake surface.
Itoigawa et al. [2006] proposed a new MQL lubricant, oil film on water droplet, to provide a large cooling ability. The nano-enhanced lubricants (nano-sized molybdenum disulfide (MoS2) particles) for MQL described in Shen et al. [2008] applied to grinding processes. However, the dissociation temperature of MoS2 is extremely low (at 350° C. in oxidizing environments), which will be a major problem for conventional machining applications.
Suda et al. U.S. Publication No. 2008/0026967 describes mixtures of oils for Minimum Quantity Lubrication (MQL). There is a suggestion of incorporating graphite in the oil but there are no examples. The problem is that the commercially available graphite is very difficult to mix with the oils after preparation by high temperature heating (800° C.-1000° C.) of the graphite over a substantial period of time. There is a need for better graphite particles which are more effective for MQL.
Objects
It is therefore an object of the present disclosure to provide a lubricant composition for use in MQL machining. It is further an object of the present disclosure to provide a method of machining using the lubricant composition at MQL process conditions. Another object is to improve the lubricity of current MQL lubricant compositions.
These and other objects may become increasingly apparent by reference to the following description.